Once upon a time, /tg/ decided to make an Imperial Guard regiment using the still-in-beta Only War rules. The first few rolls established the regiment in question as an urban/siege fighting unit, with a bilious commander (giving them the Paranoia talent). And then a percentage die was rolled to see how many of the unit that were psykers, and somebody got a 97.
Such was born the 1st Membranes (colloquially known as the 'Exploding Brains' or 'Emperor's Powder-Kegs'), a unit created when an Inquisitorial Black Ship crashed on a small forge world, with the psyker cargo spilling out and mingling with the population. Many of the psykers were absorbed into the Imperial Guard regiment stationed there, resulting in an unprecedented 97% psyker population in the regiment (a smaller percent exists in the population at large). The 1st Membranes have fought campaigns against Tau and Orks (in one notable battle fighting against the Scraploota Ork clan, also created by /tg/), as well as putting down the daemons that the men keep accidentally summoning.
At any point in time, you've got Guardsmen hearing voices, Guardsman thinking they're horses, Guardsmen thinking they're Sanguinius reborn, and Guardsmen exploding into tentacles, boils, and boiling tentacles at the slightest provocation. Almost everyone is crazy, and those who aren't probably will be soon.
- Canon Defilement: In-Universe example. There's pretty much no way an almost all-psyker regiment could exist in canon, but that's part of the fun.
- Action Bomb: Regarded as a regiment-wide version of this by the Genre Savvy command staff of the Guard.
- Army of Thieves and Whores: What happens when a primarily Adeptus Mechanicus planet donates a crapton of psykers to the Guard.
- Bad Boss: Their bilious leader, Tiberius the psyker commissar.
- Blessed with Suck: Who wouldn't want an entire legion of gun-toting psychics? A setting where Magic Is Evil, that's where.
- Body Horror: Happens a lot when Guardsmen lose control of their powers.
- Demonic Possession: Incredibly common, since they're almost all not-fully-trained psykers.
- Doom Magnet: Sergent Revok of the 13th company keeps surviving while all the rest of his unit dies. It's represented in stats through his Suspicious Fate rule.
- Eldritch Abomination: The regiment has a habit of accidentally summoning them.
- Genre Savvy: Why they're kept to backwater worlds; the command staff knows very well the entire regiment suffers from destructive Power Incontinence.
- Go Among Mad People: Tends to happen to the few sane ones in the regiment.
- Hearing Voices: Brian Consumptington.
- Humongous Mecha: The regiment has four Imperator-class Titans.
- Mage Marksman: The defining trait of the Membranes.
- Obvious Beta: The reason for the regiment's existence is that some bright spark in charge of making Only War rules thought it would be a good idea to roll a percentile die to determine how many psykers a regiment had.
- Only Sane Man: The few without psychic powers tend to be this.
- Psychic Powers: Almost everyone has them, with the 3% that don't mostly being officers.
- Shock and Awe: Can use their powers for this.
- Tinfoil Hat: It helps stop the majority of whispers from the Warp.
- With Great Power Comes Great Insanity: Standard for Warhammer 40k psykers.